The deep ocean is a wild place where unusual creatures live with very little light. We used to think these zones were sparsely populated, but a new study from a team of international marine biologists says that the mesopelagic zone from 100-1000m below the surface — and far from shore — is teeming with life.

Fish species that call the mesopelagic zone home usually come closer to the surface at night to feed. By diving back down at dawn, they avoid predators like birds (and people). Living at these depths has resulted in the evolution of larger eyes and more sensitivity to changes in pressure. As a result, these creatures are quite adept at dodging nets. They can spot them as far out as five meters — long enough to avoid even the widest nets.

Nets aren’t just for commercial fishermen, though. Netting fish is also how marine biologists sample the ecosystem and estimate the fish population. Because these fish are less likely to show up in nets, we always thought the mesopelagic zone was a desert.

The team making these new counts of fish populations used sonar-based tools as a stand-in for traditional nets. They found 10-30 times more fish in the mesopelagic zone than expected. If these numbers hold up to scrutiny, that would mean 95% of the world’s fish biomass lives in the mesopelagic zone where they have been virtually untouched by fishermen. That would mean the oceans are much healthier than previously thought. We might even have a path toward sustainable fishing if our estimates of fish populations were off by that much.